Invega is prescribed for treatment of Schizophrenia. According to its label, “The mechanism of action of paliperidone, as with other drugs having efficacy in schizophrenia, is unknown, but it has been proposed that the drug's therapeutic activity in schizophrenia is mediated through a combination of central dopamine Type 2 (D2) and serotonin Type 2 (5HT2A) receptor antagonism.

ADDICTION / DEPENDENCE

HALF LIFE AND METABOLISM

The biological half life of a substance is the time it takes for a drug to lose half of its pharmacologic activity. This is significant because it affects how soon withdrawal symptoms may appear.

The half life of Invega is approximately 23 hours.

Invega is mainly metabolized through the P450 pathway in the liver and the enzymes primarily handling the metabolism are CYP3A4 and CYP2D6.

The CYP enzymes are the major enzymes involved in drug metabolism, and since many drugs may increase or decrease the activity of various CYP isozymes, this is a major source of adverse drug interactions, since changes in CYP enzyme activity may affect the metabolism and clearance of various drugs. For example, if one drug inhibits the CYP-mediated metabolism of another drug, the second drug may accumulate within the body to toxic levels, possibly causing an overdose.

BLACK BOX WARNING

The Food and Drug Administration (FDA) has decided that some drugs pose very serious risks and have required these drugs have what is called a black box warning. Invega has a black box warning. Here is the warning.

Elderly patients with dementia-related psychosis treated with antipsychotic drugs are at an increased risk of death. Analyses of seventeen placebo-controlled trials (modal duration of 10 weeks), largely in patients taking atypical antipsychotic drugs, revealed a risk of death in drug-treated patients of between 1.6 to 1.7 times the risk of death in placebo-treated patients. Over the course of a typical 10-week controlled trial, the rate of death in drug-treated patients was about 4.5%, compared to a rate of about 2.6% in the placebo group. Although the causes of death were varied, most of the deaths appeared to be either cardiovascular (eg, heart failure, sudden death) or infectious (eg, pneumonia) in nature. Observational studies suggest that, similar to atypical antipsychotic drugs, treatment with conventional antipsychotic drugs may increase mortality. The extent to which the findings of increased mortality in observational studies may be attributed to the antipsychotic drug as opposed to some characteristic(s) of the patients is not clear. ABILIFY (aripiprazole) is not approved for the treatment of patients with dementia-related psychosis [see WARNINGS AND PRECAUTIONS (5.1)]. Antidepressants increased the risk compared to placebo of suicidal thinking and behavior (suicidality) in children, adolescents, and young adults in short-term studies of Major Depressive Disorder (MDD) and other psychiatric disorders. Anyone considering the use of adjunctive ABILIFY or any other antidepressant in a child, adolescent, or young adult must balance this risk with the clinical need. Short-term studies did not show an increase in the risk of suicidality with antidepressants compared to placebo in adults beyond age 24; there was a reduction in risk with antidepressants compared to placebo in adults aged 65 and older. Depression and certain other psychiatric disorders are themselves associated with increases in the risk of suicide. Patients of all ages who are started on antidepressant therapy should be monitored appropriately and observed closely for clinical worsening, suicidality, or unusual changes in behavior. Families and caregivers should be advised of the need for close observation and communication with the prescriber. ABILIFY is not approved for use in pediatric patients with depression [see WARNINGS AND PRECAUTIONS].

SIDE EFFECTS

The following information is taken from the Invega label:

abdominal pain

akathisia

anaphylactic reaction

asthenia

atrioventricular block

bundle branch block

cerebrovascular accidents

diabetes mellitus

dizziness

dry mouth

dysphagia

dystonia

edema

extrapyramidal disorder

fatalities

fatigue

first degree bradycardia

headache

hyperglycemia

hyperprolactinemia

hypertonia

ischemia

neuroleptic malignant syndrome

orthostatic hypotension

palpitations

parkinsomism

salivary hypersecretion

sedation

seizures

sinus arrhythmia

somnolence

swollen tongue

syncope

tachycardia

tardive dyskinesia

transient ischemic attacks

tremor

abdominal pain upper

WITHDRAWAL SYMPTOMS

Invega can be a very difficult drug to stop taking.

agitation

anorexia

anxiety

attention deficit hyperactivity

autism

diarrhea

emesis (vomiting)

insomnia

itching

mood swings

muscle pain

nausea

post-partum depression

restlessness

rhinorrhoea (runny nose)

sleep disruption

sweating

TREATMENT

Withdrawal from Invega should only be done under the care of a health practitioner. The safest way is to withdraw at an inpatient medical detox facility. At an inpatient medical detox facility with a protocol that includes hydration, vitamins and supplements, most patients can safely stop taking Invega in about seven days. Patients can withdraw from Invega on an outpatient basis but it will normally take at least four weeks.